: When we flush the toilet we get air bubbling up out of the soil pipe. This used to cause a faint odor of sewer gas. The toilet gets clogged at least once a week. We have removed and replaced the bowl and it did not help. The upstairs toilet (which uses the same vent) works fine. We could not find anything in the trap. Any advice?

This is not a vent problem. You most likely have a clog in the drainage line. This generally takes a large power auger to clear.DebThe Pipewench